The acquisition of rules for formulating causative verbs was studied with children over a period of a few years. Most of the data is based on the spontaneous speech of the author's two daughters, from age 2;6 to 6;2 and from age 2;4 to 3;11. It was hypothesized that there are at least two prerequisites for the child's formulation of a general rule for converting noncausative predicates into simple causative sentences: (1) achievement of an underlying representation in which the semantic material conflated by the rule is spelled out relatively explicitly and (2) knowledge of some unanalyzed, memorized forms patterned according to the rule. It is concluded that in acquiring their lexicon children seem to be doing more than just working out the meanings of individual words. The child has rather abstract information about what lexical items are possible in her language, which allows her to predict, sometimes erroneously, that words with certain meanings will exist. The child's analysis of the semantic structure of her words seems to proceed in rather close conjunction with syntactic development. The close-to-simultaneous emergence of periphrastic (unconflated) causative sentences and their conflated counterparts at two stages of development in the study data suggests that sentences of both kinds are ultimately related to the same underlying structure. It is the achievement of this structure that allows the child to acquire a productive control over the variety of surface realizations of it that her language offers. (SW)